iframe offers sandbox to your data. it allows websites to show info such as your email address from Google or services without said websites knowing your addres

iframe offers sandbox to your data. it allows websites to show info such as your email address from Google or services without said websites knowing your address. or to like a tweet with your account. or to leave a comment through Facebook. or to display targeted ads. or to enter credentials with somewhat safer environment. I say somewhat because it is safer done right but there will always be people entering their private crypto keys that totally throw off the statistics.